Seeing red - our key to survival

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Human colour vision developed as a result of our primate ancestors' need to distinguish red from green in order to get the best leaves, new research has found.

Nathaniel Dominy and Peter Lucas at the University of Hong Kong argue in this week's Nature that primates developed this ability in order to locate the most nutritious food in the forest.

For well over a century, researchers have thought that human colour vision (trichromatic vision - the ability to see red, green and yellow/blue light) developed in our primate ancestors in response to their need to recognise the colour of favourite fruits.

However Dominy and Lucas observed the eating habits of four species of Old World (only found in Africa and Asia) primates with trichromatic vision in Uganda's Kibale Forest and found that choosing fruit only required the more primitive, dichromatic vision - the ability to see yellow/blue light.

Red-green vision, however, was needed to distinguish young tender leaves from tougher, less palatable leaves. In Old World tropical forests, younger leaves tend to have a reddish tinge in contrast to a generally green environment.

The researchers argue that because these young leaves are an important protein source at the time of the year when fruits are scarce, red-green vision gave our ancestors a survival advantage over other primates.

"It sounds quite plausible," animal behaviour expert Professor Lesley Rogers of the University of New England told ABC Science Online. "But there's another variable that should be put into the equation."

Professor Rogers points out that our nearest ancestors - the chimpanzees and orangutans - supplement their diet with insects which are easier to see with dichromatic vision which enhances the ability to distinguish texture and movement.

"People seem to assume that evolution necessarily means going to something better," she said. "But when Old World primates traded off the ability to see texture and movement well for full colour vision you might have expected them to have given up eating insects."